Self-starting synchronous motor



July 14,1925. 1,546,269

H. E. WARREN I SELF STARTING SYNCHRONOUS MOTOR Filed Sept. 11, 1922 FTQI.

2 l0 .3 6 7 kh T Inventor: H envy ETWarPen ymfl H i s Attorn ey a citizen of the United States,

Patented July 14, 1925.

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A lication filed September 11, 1922. Serial Io. 7,216.

To all whom it concem:

Be it known that I, HENRY E. WARREN, residing at Ashland, count .of Middlesex, State of Massachusetts, ave invented certain new and useful Im rovements in Self-Startin Synchronous otors, of which the followin is a specification.

y invention relates to self start1ng synchronous motors and more in particular to improvements in the rotor of such motors as is described in my copending a plication, Serial No. 521,590 entitled Se f-starting synchronous motors filed December v12, 1921, and assigned to the same assignee as the resent invention.

T e motor described in the above mentioned application comprises a stationary alternating current field member having interleaved shaded pole pieces for producing a rotating magnetic field and a rotor mounted within said field consisting of one or moregsplit rings of permanent magnet material suitably supported on a s ider and shaft. This rotor is capable 0 starting from rest and revolving in exact synchronism with the rotating magnetic field.

The motor of my present application comprises means for producing a rotating magnetic field preferably similar tothe means described in ap lication, Serial No. 521,590 and a rotor ma e of one or more symmetrical stampings of ermanent ma net material which have the se f-starting an synchronizing characteristics of the split ring rotor above referred to, but which do not require a separate spider for their support. The rotor of m present application combines in an integra structure a continuous ring with radial arms arran ed on the polar axes, said arms producing t e synchronizing characteristics and constituting the rotor spider. This construction always produces a me chanically balanced rotor irrespective of the number of rotor units used on the same shaft. In the bi-polar, or preferred form, the synchronizing portion 0 therotor comprises a diametrically disposed bar. This type of. rotor combines the self-starting characteristics of a ring and the synchronizing characteristics of a bar irra single member. The characteristics of the motor may be altered by changing the relative dimensions of the ring and olar portions of the rotor. Furthermore, 1 have found that at g vantages of my improved motor-will appear as the description proceeds.

The features of my invention which I believe to be novel and patentable will be inted out in the claims appended hereto. he details of construction and manner of operation of myimproved motor will now be explained in connection with the accompanying drawing in which Fig. 1 illustrates an end view of a bi polar motor with the rotor in place; Fig. 2 represents a sectional view taken on line A-A of Fi 1 looking in the direction of the rotor; an end view of the rotor member removed; and Fig. 4 shows a plan View of the same.

Referring to Fig. 1, I have shown a type of self-startin synchronous motor in which a bi-polar field magnet 1 is provided with a predominant characteristic is deig. 3 shows single phase energizing winging 2 and with shading coils 3 and 4 for causing a time lag of the magnetic flux in pole faces 5 and 6 behind that in the pole faces 7 and 8. The rotor element comprises one or more stampings of sheet steel or other permanent magnetic material each consisting of a continuous ring 9 with a bar 10 across one diameter. The center of the bar is enlarged and provided with an opening .to form a hub 11 for concentrically mounting the rotor on a shaft 12. This type of rotor requires no additional spider structure, is mechanically balanced and is very inexpensive since the entire rotor element may be stamped from sheet metal by one operation and then pressed or otherwise fastened on the shaft.

The ring portion of such a structure when placed in a rotating magnetic field has stron starting characteristics and weak synoc ronizing characteristics similar to that of an induction motor. Thebar or polar portion, however, has a strong tendency to remain at rest but when once brought up to near synchronous speed with the rotating magnetic field, it becomes permanently magnetized and has strong synchronizing characteristics similar to that of a straight synchronous motor. When at rest the rotor position of least reluctance is that shown in Fig. with the bar ortion and ring forming parallel paths for t e magnetic ring portions.

flux zind this is the position the rotor will take in a weak field. Ina rotating ma netic field such as produced by the fi e (1 structure here shown when at rest the rin portion attempts to follow the rotatmg field but the bar portion tends to maintain 1ts position of least reluctance. I have found that the behavior of the rotorat rest apparently depends upon the relative amount of magnetism necessary to saturate the bar and lhus, I have found that with a comparatively weak field of the proper form for the operation of the motor, this rotor will not start. It tends to behave like a plain bar occupyin the position of least reluctance due, I be ieve, to the fact that the ma'or portion of the flux passes through the ar. As the strength of the al-. ternatin magnetic field is increased, the bar portion ecomes saturated and a greater proportion of the flux passes throu h the ring until a point is reached where t e tendency of the bar to resist rotation is overcome by the tendency of the ring to rotate, which causes the rotor to start and then, of course, it ver quickly reaches synchronous speed. En still stronger fields, the tendency to start is greatly increased so that the opposition of the-bar to starting becomes comparatively negligible. After synchronousspeed is reached the motor voltage may be reduced to a value below that necessary to start the motor without reducing the motor speed. It will thus be seen that this feature makes ssible the use of my motor as a selective evice on a variable voltage alternating current system. Furthermore, by suitably proportioning the relative cross-sectional areas of the bar and ring portions of difierent motors on the same system, said motors may be made to start at difierent selective voltages. The preferred type of field structure for producing the rotating magnetic field is described and claimed 1n my co-pending application Serial No. 521,590 above referred to. Thisffield is built of laminations as shown in Fig. 2 and has polar projections v5, '8, 7 and 8 in which all of the laminations are used. There is a very considerable air ga iromthe solid pole place 5 to the solid po e piece 8 and likewise between pole ieces 6 and 7. Across this gap a few of the aminations are allowed to overlap as 13 and it from the right hand portion of the field and 15 and 16 from the left hand portion. A suitable air gap is provided between and around these overlappinglaminations so as not to short circuit the opposite sides of the field and'so as to leave a zone around the rotor in which the magnetic lines from one pole aresomewhat mixed with the'magnetic lines from the opposite pole. The magne-- tism in poles 5 and 6 lags somewhat behind that in the unshaded poles 7 and 8, but this angle oflag is considerably less than 90.

1 in 5 because the 1a of the pole 8 is 180 dedegrees. Owing, however, to the mixed magnetism in the zone where the laminations overlap, there is a tendency to produce there a field which lags still further behind that grees behind 7. n the construction de scribed the overlapping laminations produce a more nearly uniform rotating magnetic field than the usual construction where the overlapping portions are omitted.

. With this construction it is feasible to use several rotor stampings on the same shaft separated by a sufiicient distance to maintain the desired relation of flux density in the rotor and overlapping stator sections. In Fig. 2 I have shown two rotor elements 9 arranged on the same shaft with the bar portions parallel or substantially so. However, I do not wish to be limited to any particular number of rotor elements. For many purposes one rotor element will be found to give sufiicient torque and for greater torques additional rotor elements may be added, increasing the width of the stator element proportionately.

found to be satisfactory for ordinary purposes. The diameter of the pole pieces of the field outside diameter of the rotor A width of ring portion 3/64"; width The material used for the ring was sixpercent tungsten magnet steel. 1 do not wish, however, to be limited .to these dimensions or to this exact dimensional relation or to the specific material mentioned, but seek to cover in the appended claims all modifications coming fairly within the true scope and spirit of my invention, including the multi-polar' motor wherein the polar portions of the rotor consist of radial arms disposed on the polar axes of the motor.

What I claim as new and desire to secure by Letters Patent of the United States 13:-

1. A self starting synchronous motor provided with means for roducing a rotating magnetic field and having a rotor consisting of one or more continuous rings of magnetic material each provided Wight integral radial ot bar portion and thickness of rotor 90 The following dimensions have been arms equal in number to the poles of the across a diameter thereof forming a spider.

3." A self starting synchronous motor pro-j videdwith means for producing a substantially uniform, rotating magnetic field a rotor for said motor comprising a plurality of spaced mechanically balanced rings of permanent magnet steel each provided with an integral bar across a diameter thereof, and

or more continuous rings of permanent magnet steel each provided with an integral bar a shaft for said motor, said bars being secured on said shaft substantially in a plane.

4. A self starting synchronous motor comprising a laminated field ma et provided with an excitin winding and cooperating, partially shaded polar projections having spaced, overlapping laminations extending from the faces thereof for producing a mixed field between the shaded and unshaded portions of adjacent pole faces, and a rotor between said pole faces, said rotor comprising one or more mechanically balanced rings of permanent magnet steel each prvided with an integral bar across a diameter thereof. I 5. A rotor for a self starting synchronous motor consisting of one or more balanced rings of permanent magnet steel each provided with integral 'radial arms equal in number to the poles of the motor and disposed on polarradii said rings forming the starting member and said radial arms the synchronizing member of said rotor.

6. A bi-polar rotor for a self starting synchronous motor comprising one or more continuous rings of ermanent magnetic steel each provided with an integral bar across a diameter thereof, the central portion of said bars being enlarged to form a hub.

7. In a self starting Synchronous motor a rotor element consisting of a continuous ring of permanent magnet steel provided wit integral radial arms disposed on polar radii,

" the cross-sectional area of said ring andarms being substantially the same.

8. A self starting synchronous motor comprising means for producing arotatin magnetic held, ing portions for producing starting and synchronizing characteristics respectively, so arranged and pro rtioned flux takes paralle paths J therethrough at starting to produce opposing torques, the torque of said portion aving the starting characharistics predominating only after said other portion becomes magnetically saturated.

9. A self starting synchronous motor comprising meansfor producin a substantially circular rotating magnetic eld, a rotor disposed in said field having portions for producing starting and synchronizing characteristics respectively, so arranged and proportioned that the rotor flux takes parallel paths therethrough at starting, the portion having the synchronizing characteristics having the least reluctance whereby said rotor will start only after said last mentioned portionv becomes magnetically saturated.

In witness whereof, I have hereunto set my hand this th day of Aug. 1922.

HENRY E. WARREN.

a rotor disposed in said fie dhavthat the rotor 

